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One trial will test sirukumab in patients that have failed an anti-tumor necrosis factor-alpha therapy: Pfizer(NYSE: PFE) and Amgen's Enbrel, Abbott Labs' (NYSE: ABT) Humira, and J&J's own Remicade. The other trial will test patients potentially earlier in disease progression. They only have to have failed a disease modifying anti-rheumatic drug, which could include methotrexate, which is typically given before the anti-TNF-alpha drugs.

Rheumatoid arthritis is gigantic market, but I wouldn't pencil in blockbuster sales just yet.

Sure, there's no cure for rheumatoid arthritis, and people fail the currently available drugs. But there's a lot of competition out there. And doctors aren't necessarily interested in switching to a new drug from something they have experience with. Bristol-Myers Squibb's Orencia is finally on pace to reach blockbuster status this year -- its seventh year on the market.

The most concerning thing about sirukumab is that it has to be injected. The up-and-coming drugs to treat rheumatoid arthritis will be taken orally. Pfizer's tofacitinib is currently under review at the Food and Drug Administration. Furthermore, both Incyte(Nasdaq: INCY) in combination with Eli Lilly, and Rigel with AstraZeneca, also have oral drugs in the works.

This doesn't seem like the best way to spend research and development dollars to me, but it's not like either company is hurting for cash. Sometimes it's worth taking a single to balance out the big swings, like the one J&J took with its Alzheimer's drug.

And who knows, maybe sirukumab will turn out to be a wonder drug, better than anything out there and with fewer side effects. Unfortunately with drug development, the only way to know is to run the clinical trials.